上文简介了HttpClient和Tomcatserver的交互，主角是HttpClient,然后它跟server交互有两种方式即get和post。所以这个HttpClient就相似于电脑上用的浏览器。当我打开多个网页的时候，并不须要开一个网页就开一个浏览器，而是一个浏览器上面开了好几个网页。相应于HttpClient，即无需连接一次就new一个HttpClient。一般，我们希望一个应用里就一个HttpClient就ok了，就像我们的手机或PC，没人会呼呼的装好几个浏览器。本文即解决此问题，代码能够直接拿过去复用。
1、自然而然想到单例。
public class MyHttpClient {
private static HttpClient mHttpClient = null;
private static final String CHARSET = HTTP.UTF_8;
//将构造函数封掉，仅仅能通过对外接口来获取HttpClient实例
private MyHttpClient(){
}
public static HttpClient getHttpClient(){
if(mHttpClient == null){
mHttpClient = new DefaultHttpClient();
}
return mHttpClient;
}
}
上面是最简单的一种单例，确实能够满足须要。但不能满足多线程的要求，即当同一时候完毕多个Http请求时，就出马蛋了。
2、线程安全的HttpClient
幸运的是android已经提供了能够创建线程安全的HttpClient，即通过ClientConnectionManager 来完毕。以下贴出完整代码：
package org.yanzi.webutil;
import org.apache.http.HttpVersion;
import org.apache.http.client.HttpClient;
import org.apache.http.conn.ClientConnectionManager;
import org.apache.http.conn.params.ConnManagerParams;
import org.apache.http.conn.scheme.PlainSocketFactory;
import org.apache.http.conn.scheme.Scheme;
import org.apache.http.conn.scheme.SchemeRegistry;
import org.apache.http.conn.ssl.SSLSocketFactory;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.impl.conn.tsccm.ThreadSafeClientConnManager;
import org.apache.http.params.BasicHttpParams;
import org.apache.http.params.HttpConnectionParams;
import org.apache.http.params.HttpParams;
import org.apache.http.params.HttpProtocolParams;
import org.apache.http.protocol.HTTP;
public class MyHttpClient {
private static HttpClient mHttpClient = null;
private static final String CHARSET = HTTP.UTF_8;
//将构造函数封掉，仅仅能通过对外接口来获取HttpClient实例
private MyHttpClient(){
}
public static HttpClient getHttpClient(){
if(mHttpClient == null){
mHttpClient = new DefaultHttpClient();
}
return mHttpClient;
}
public static synchronized HttpClient getSaveHttpClient(){
if(mHttpClient == null){
HttpParams params = new BasicHttpParams();
//设置基本參数
HttpProtocolParams.setVersion(params, HttpVersion.HTTP_1_1);
HttpProtocolParams.setContentCharset(params, CHARSET);
HttpProtocolParams.setUseExpectContinue(params, true);
//超时设置
/*从连接池中取连接的超时时间*/
ConnManagerParams.setTimeout(params, 1000);
/*连接超时*/
HttpConnectionParams.setConnectionTimeout(params, 2000);
/*请求超时*/
HttpConnectionParams.setSoTimeout(params, 4000);
//设置HttpClient支持HTTp和HTTPS两种模式
SchemeRegistry schReg = new SchemeRegistry();
schReg.register(new Scheme("http", PlainSocketFactory.getSocketFactory(), 80));
schReg.register(new Scheme("https", SSLSocketFactory.getSocketFactory(), 443));
//使用线程安全的连接管理来创建HttpClient
ClientConnectionManager conMgr = new ThreadSafeClientConnManager(params, schReg);
mHttpClient = new DefaultHttpClient(conMgr, params);
}
return mHttpClient;
}
}
方法getSaveHttpClient()就可以获得线程安全的单例httpClient，凝视非常具体了啥都不说了，能够直接使用。
3、已经非常完美了，还能不能再优化呢?
能够使用Application来进一步优化创建HttpClient的时机及其它配置。Application的相关知识參见:链接
新建包名org.yanzi.application，在里面新建MyApplication.java，完整代码例如以下:
package org.yanzi.application;
import org.apache.http.HttpVersion;
import org.apache.http.client.HttpClient;
import org.apache.http.conn.ClientConnectionManager;
import org.apache.http.conn.params.ConnManagerParams;
import org.apache.http.conn.scheme.PlainSocketFactory;
import org.apache.http.conn.scheme.Scheme;
import org.apache.http.conn.scheme.SchemeRegistry;
import org.apache.http.conn.ssl.SSLSocketFactory;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.impl.conn.tsccm.ThreadSafeClientConnManager;
import org.apache.http.params.BasicHttpParams;
import org.apache.http.params.HttpConnectionParams;
import org.apache.http.params.HttpParams;
import org.apache.http.params.HttpProtocolParams;
import org.apache.http.protocol.HTTP;
import android.app.Application;
public class MyApplication extends Application {
private HttpClient mHttpClient = null;
private static final String CHARSET = HTTP.UTF_8;
@Override
public void onCreate() {
// TODO Auto-generated method stub
super.onCreate();
mHttpClient = this.createHttpClient();
}
@Override
public void onTerminate() {
// TODO Auto-generated method stub
super.onTerminate();
this.shutdownHttpClient();
}
@Override
public void onLowMemory() {
// TODO Auto-generated method stub
super.onLowMemory();
this.shutdownHttpClient();
}
/**创建HttpClient实例
* @return
*/
private HttpClient createHttpClient(){
HttpParams params = new BasicHttpParams();
//设置基本參数
HttpProtocolParams.setVersion(params, HttpVersion.HTTP_1_1);
HttpProtocolParams.setContentCharset(params, CHARSET);
HttpProtocolParams.setUseExpectContinue(params, true);
//超时设置
/*从连接池中取连接的超时时间*/
ConnManagerParams.setTimeout(params, 1000);
/*连接超时*/
HttpConnectionParams.setConnectionTimeout(params, 2000);
/*请求超时*/
HttpConnectionParams.setSoTimeout(params, 4000);
//设置HttpClient支持HTTp和HTTPS两种模式
SchemeRegistry schReg = new SchemeRegistry();
schReg.register(new Scheme("http", PlainSocketFactory.getSocketFactory(), 80));
schReg.register(new Scheme("https", SSLSocketFactory.getSocketFactory(), 443));
//使用线程安全的连接管理来创建HttpClient
ClientConnectionManager conMgr = new ThreadSafeClientConnManager(params, schReg);
HttpClient client = new DefaultHttpClient(conMgr, params);
return client;
}
private void shutdownHttpClient(){
if(mHttpClient != null && mHttpClient.getConnectionManager() != null){
mHttpClient.getConnectionManager().shutdown();
}
}
public HttpClient getHttpClient(){
return mHttpClient;
}
}
然后再AndroidManifest.xml理加入：
android:name="org.yanzi.application.MyApplication"
<application
android:name="org.yanzi.application.MyApplication"
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="org.yanzi.testtomecat.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>然后再Activity里，通过mMyApplication = (MyApplication)getApplication();
mMyApplication.getHttpClient()得到HttpClient就能够使用了。
能够看到在Application的onCreate里就实例化了HttpClient，且在低内存和关闭时关闭连接管理器，释放资源，比2中的写到一个普通文件中更优。